A characterization of the 1/12 subunit of erythrocruorin is presently being conducted. Isolation from the intact molecule is possible by gel filtration at alkaline pH. Molecular weight will be determined by sedimentation equilibrium ultracentrifugation. The number of copies of the 50,000 MW peptide in the 1/12 subunit will be determined using quantitative polyacrylamide gel electrophoresis. Cross-linking experiments will be performed to examine the topology of the subunit.